The best game to ever mix the action and RPG genres is Crimsonlands. When the original freeware version came out it incited a huge thread of praise, score bragging, and philosophical analysis at OMM. The man game mode, "survival," is Robotron 2084 with you facing an endless onslaught of tougher, faster, and more numerous monsters. Controls are move with the keyboard and aim/shoot with the mouse.

The hook is that your score is measured in experience points and when you level up you can pause the game and pick from five randomly chosen "perks" ala. GURPS/Fallout. No stats or die rolls or other abstract nonsense. These perks range from the utilitarian "load your gun faster" to the strangely useful "emit deadly radiation" to the grim "die now and increase your score by 20%" So in addition to the nonstop blasting and the body counts in the quadruple digits, there's a real mindfuck strategy game of how to build your character up balancing survivability and experience accumulation to face your inevitable death with the highest score.

Sadly, once you got the hang of it you realized the weapons were horribly unbalanced and there was only one "right" way to get a high score. You can still snag the freeware version here.

Since then the author expanded it and balanced it and made it into a $20 shareware game. Is it better? Yes and no. The good is there are zillions of interesting and creative new weapons (gauss shotgun, anyone?) fixed balance issues (sawed-off shotgun is not longer teh ultimate, mean minigun is now practical, flamethrower and blowtorch still suck, though) and threw in a fuckload of new perks, including perks that heal you! There are now many different strategies that will net you a high score, and hours and hours of replay!

The bad is that the designer fell into trap of including what may become the "unnecessary FPS jump puzzle" of the 21st century: Mandatory Unlockables! The vast majority of the weapons and perks start out locked and you MUST play through 50 "quest missions" (you verses a fixed number of enemies) to finally be able to play survival mode as it was meant to be played. Now to be fair these quests can be pretty fun sometimes on their own, but this is supposed to be a 15-minute-violence-fix-arcade-game and I just paid frikkin' MONEY for it. Gimme all the fun stuff now!

Whichever version you get, I guarantee fun. If you have a couple hours to unlock everything, the shareware version is superior. Score bragging in the death threats forum!